A quick diversion into metal polishing. I transferred into the polishing department in October of 1988 in order to get back on first shift. There seemed no hope of me achieving this anytime soon as a flanger operator, and I felt I needed to be at home with my sons at night. The first job I bid on was press operator. Geoff L. didn’t want me to stop operating a flanging machine. But I had way more seniority than anyone else who bid on the job. So he took the bid down without filling it. That’s what he did when someone he didn’t want to get the job was going to be awarded the job. The next job to go up on the board was polishing. I bid on that one, too, and once again I had way more seniority than anyone else who bid. Now he realized I was determined. So I got this job. I went onto second shift for a week to train with John R. He was in his fifties, and had been a metal polisher all his life. He was an excellent polisher and an excellent instructor. In a week’s time he got me started with the basics: the different grit belts to use for which finishes, how to set up and operate the polishing machine, how to check the finish for smoothness once you were done with an rms indictor. The device pictured below is similar to the one we used.
Some quick basics about metal polishing. Customers either requested a certain grit finish, such as 80 grit, which wasn’t too fine, or a certain reading on the rms indicator. The most common reading requested was 15-25 rms. Which means a reading taken against the grain can be no higher than 25, while a reading taken with the grain could be no higher than 15, the grain being the direction of the belt across the metal being polished. Some customers requested a 4-8 rms reading on the finished product. That is smoother than glass. These heads were going onto tanks for a pharmaceutical company, to be used for processing medicine. The tanks were thoroughly cleaned between batches, and there could be no imperfections in the metal for bits of liquid to be caught in. A reading as fine as this required many hours of going over and over the surface with our lightest-grit belts, which were 320-grit. We would wear one such belt down, greasing it well and adding polishing fluid into the head, and use it until the required finish was achieved. If we broke such a belt, we would hopefully have an old used one on hand we had saved for just such an occurrence, if not we would have to start over with an new 320. We even had one customer request a 0-4 rms reading. Which was ridiculous, I have never gotten a reading of 0 on the indicator. We just got it as low as we could and let it go.
There were two polishing machines, a large and a small. There was an electric turntable upon which the head sat. And it had to sit level. If the head had a center hole, there was no problem in lining it up. But if the head was a no hole, lining it up was tricky. You put two screw clamps on the head, put a two-way chain on the hook of an overhead crane, lifted the head onto the turntable, then wrestled it around until it rested level. Next, you started with a heavy grit belt, such as a 50. We had a heavier grit belt, a 36, but that was never used on a head with a high-grit finish. The 36 would leave grit lines in the finish that the 50 couldn’t get out. So most of the time we’d start with a 50. The arm of the polishing machine was spring-loaded. We’d release the pressure, slackening the arm to put the belt on, then adjust the pressure back up, extending the arm back out and stretching the belt tight. Then we’d start at the edge of the head and work our way to the center. You never wanted to hit the center with a new belt, it was easy to thin out the center that way. So as the head revolved on the turntable, you started the belt to spinning, then maneuvered the arm inside the head, bringing the polishing belt against the edge of the spinning head lightly, then started it on its way toward the center, adjusting the air pressure as you went, to control how hard the belt bore down on the spinning metal.
This was tricky machine to operate. If you hit the spinning head at the edge with too much pressure, you could either throw or break the belt. If you used too much pressure while the arm was moving toward the center, the same could happen. If you used too little pressure, you weren’t doing much polishing. There were all kinds of difficulties. If for some reason the arm stalled in moving toward the center of the head, it would polish a ring in the head that you couldn’t get out. Also, these were pressed and flanged heads we were polishing, which meant they weren’t perfectly round, and could have humps and wrinkles in them. Now as the arm traveled toward the center, you had to increase the speed of the turntable and the speed of the arm, because you were covering less and less surface.
You kept using 50-grit belts, like the one pictured below, until you reached the point where most of the pits and scratches and other imperfections in the metal surface were gone.
That’s when you climbed down into the machine on your hands and knees and searched out all the remaining imperfections, and ground them out with a patent wheel.
You always used a lighter-grit belt, usually an 80 but sometimes a 120 if the finish was to be very fine. Then you went back over the head with one more 50-grit belt in order to blend in the places you had hand-polished. Now you were ready to start finishing the head. Next came an 80-grit belt, being sure to cover up all the 50-grit lines. Then came the 120-grit belt. These you started greasing, to get a smoother finish. Most of the time you ended up with a 180-grit belt, to get a 15-25 rms reading. Of course, you might have to go over the head several times with a worn 180 belt in order to achieve this reading. For finer finishes, you continued on with a 220-grit belt or on to a 320, whatever was required. We even had a Scotch-Brite belt for really shiny finishes.
As you can tell, I’m just getting started on metal polishing. It will take several posts to cover this topic.